Istituto di Geoscienze e Georisorse     
Toffanin F., Agnini C., Fornaciari E., Rio D., Giusberti L., Luciani V., Spofforth D., Palike H. Changes in calcareous nannofossil assemblages during the Middle Eocene Climatic Optimum: Clues from the central-western Tethys (Alano section, NE Italy). In: Marine Micropaleontology, vol. 81 pp. 22 - 31. Elsevier, 2011.
We present a study focused on changes in calcareous nannofossil assemblages of the Alano section during the Middle Eocene Climatic Optimum (MECO). This warming event is characterized by a prominent perturbation both in oxygen and carbon stable isotopes around the Chron C18r-C18n transition (ca. 40. Ma) and lasting ca. 500-600. kyr. Semi-quantitative analyses on calcareous nannofossil assemblages have been carried out. Our results show that the MECO interval coincides with a significant shift in the relative abundance of calcareous nannofossil taxa, suggesting a relationship between biotic changes and stable isotope shifts. Paleoecological studies at species level and/or based on morphometric criteria (i.e., small placoliths) sometimes show the opposite behavior between changes observed at the genus level and those observed at lower taxonomic levels. For instance, a taxon thought to be better adapted to oligotrophic/warm waters, e.g. Sphenolithus, shows a prominent decrease if analyzed at genus level, but an increase was instead recorded for S. spiniger. Moreover, taxa preferentially thriving in eutrophic/cold waters, as for instance small reticulofenestrids, increase remarkably in abundance during this warming phase, while medium-large placoliths do not show any significant trend. An increase in reworked, mainly Cretaceous, specimens is also observed during the MECO. These lines of evidence are consistent with a transient enrichment in dissolved nutrients in warmer sea surface waters suggesting that an enhanced nutrient availability could have driven the make-up of the calcareous nannofossil assemblages. The increase in reworking may indicate an increase in terrigenous input, due to increased chemical weathering likely produced by an enhanced hydrological cycle.
URL: http://https://www.journals.elsevier.com/marine-micropaleontology
Subject calcareous nannofossils
middle eocene climatic optimum

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